wrap mesh around other meshes (like a skin)
Blender does not have automated skinning tools to make a wrapped mesh around other (intersecting/non-manifold/etc..) meshes.

You want to voxelize such meshes, add all the volumes together and turn the volume back to a mesh. You will find this functionality in programs like Zbrush or Houdini.

In Blender there are 2 workarounds:


use metaballs as dupliverts for the mesh vertices. This will create an inflated representation of the mesh (based on the metaball size) that is a single water-tight surface (if the metaballs are big enough so there are no holes). The denser the geometry, the smaller the metaballs can be and the smaller the inflation. Convert metaballs to mesh and then you can shrink the mesh to maintain the original volume. However this results in the surface being smoothed.
use CubeSurfer addon - similar functionality as metaballs. Since metaballs were optimized performance-wise, this is in most cases slower to compute.


There is also the possibility to manually retopologize all the meshes together. A shrinkwrap modifier can help with wrapping this created skin mesh around surfaces.

You can also edit all the pieces to be water-tight and manifold and then use Blender's booleans to unify them together.